Double-Rydberg anions: Predictions on NH(3)AH(n)(-) and OH(2)AH(n)(-) structures

Double-Rydberg anions consist of a closed-shell cationic core and two elect rons in diffuse orbitals. In addition to the already characterized tetrahed ral NH4- and pyramidal OH3-, the list of stable double-Rydberg anions inclu des members of the NH3R- and OH2R- sets (where R = F, OH, NH2, and CH3) con sidered here. Double-Rydberg isomers of NH3OH-, NH3 NH2-, NH3CH3-, and OH2C H3- are stable minima in their potential energy surfaces and have positive, vertical electron detachment energies. Similar structures have been found for the corresponding neutrals, which all have adiabatic electron affinitie s that are greater than zero. Dyson orbitals pertaining to the least bound electrons of the NH3R and OH2R- anions are distributed chiefly outside the N-H and O-H bonds of the tetrahedral nitrogen and pyramidal oxygen atoms.